Torsional splitting and the four-fold barrier to internal rotation: The rotational spectra of vinylsulfur pentafluoride

W Orellana; Susanna L Stephens; Wallace C Pringle; Peter Groner; Stewart E Novick; S A Cooke

doi:10.1063/1.5050021

Torsional splitting and the four-fold barrier to internal rotation: The rotational spectra of vinylsulfur pentafluoride

J Chem Phys. 2018 Oct 14;149(14):144304. doi: 10.1063/1.5050021.

Authors

W Orellana¹, Susanna L Stephens¹, Wallace C Pringle¹, Peter Groner², Stewart E Novick¹, S A Cooke³

Affiliations

¹ Department of Chemistry, Wesleyan University, Middletown, Connecticut 06459, USA.
² Department of Chemistry, University of Missouri-Kansas City, Kansas City, Missouri 64110, USA.
³ Natural and Social Science, Purchase College SUNY, Purchase, New York 10577, USA.

PMID: 30316255
DOI: 10.1063/1.5050021

Abstract

Vinylsulfur pentafluoride (VSPF), a molecule with a four-fold internal rotor, -SF₄, has been studied with high resolution Fourier transform microwave spectroscopy. We believe that this is the first report of resolved four-fold internal rotation. As such, we have presented the tools needed to understand and analyze such a problem. These include debugging the ERHAM computer program necessary to fit the spectra and the free rotor to high barrier correlation diagram necessary to understand the torsional states of the four-fold rotor. The A, E, and B torsional state rotational transitions are well resolved and assigned. Spectroscopic transitions of four isotopologues of VSPF, H₂C=CH-SF₅, the normal isotopologue, and the singly substituted ³⁴S and ¹³C isotopologues were measured and assigned. Contrary to expectation, the A torsional state could not be fit with only a semi-rigid Hamiltonian. The barrier to internal rotation, V ₄, is found to be 227 cm^-1. Ab initio calculations at the MP2 aug-cc-pVQZ level of theory and basis set were performed and the results of this calculation are compared to our experimental results.